Asymmetric volume booster arrangement for valve actuator

ABSTRACT

An asymmetric volume booster assembly includes an actuator movable in a first direction and a second direction, a first booster in fluid communication with the actuator, and a second booster in fluid communication with the actuator. The first booster includes a first supply passage and a first exhaust passage, wherein the first supply passage supplies fluid to the actuator and the first exhaust passage exhausts fluid from the actuator. The first exhaust passage is configured to produce a first fluid flow resistance. The second booster includes a second supply passage and a second exhaust passage, wherein the second supply passage supplies fluid to the actuator and the second exhaust passage exhausts fluid from the actuator. The second exhaust passage is configured to produce a second resistance to fluid flow. The first fluid flow resistance is greater than the second fluid flow resistance, such that the actuator moves substantially symmetrically in the first direction and the second direction.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.60/562,905 filed on Apr. 16, 2004.

FIELD OF THE INVENTION

The present invention relates generally to control valve systems and,more specifically, to a volume booster arrangement with an asymmetricflow pattern for use with a valve actuator of a control valve.

BACKGROUND OF THE INVENTION

Valve systems for controlling the flow of liquids and/or gases, such ascompressed air, natural gas, oil, propane, or the like, in a processsystem are generally known in the art. These systems can employ controlvalves to prevent or inhibit pressure surges within the fluids that canotherwise cause damage to components or disrupt system function.

In one application, a compressor increases the pressure of air flowingin the process system under normal operating conditions. If demanddecreases, such as when a downstream throttling valve is closed, theneed for a portion of the air decreases rapidly, and the flow throughthe compressor decreases. When the flow decreases enough, the compressorenters an unstable condition in which gas flows backwards through thecompressor from the outlet side to the inlet side. At this point, theflow of gas oscillates rapidly between forward flow and reverse flow.This phenomenon is known as surge and is undesirable because it putsundue stress on the compressor components, such as blades and bearings.

Surge is generally addressed by the placement of a control valve aroundthe compressor that diverts flow from the outlet of the compressor tothe inlet when the compressor is near an operating point at which surgeoccurs. A control valve must act quickly because surge is a fast,unstable flow phenomenon. Traditionally, control valves have been on/offdevices. However, with the advances in automation software andelectronics as well as increased compressor sizes, significantimprovements in operating efficiency and reliability can be attained ifthe control valve is instead a throttling device. To fully realize thebenefits of a throttling valve instead of an on/off valve and to protectthe compressor against surge, the position of the valve must becontrolled both quickly and accurately.

The position of the control valve is normally controlled by apositioner. Large volume actuators can take 10 or 20 seconds or more toopen or close the control valve with a standard positioner. Such a valvepositioner cannot operate at, or deliver adequate volumes of fluid formoving the actuator at, the desired response times for optimalantisurge.

To address this problem, a control valve assembly can incorporate volumeboosters in conjunction with the positioner on a throttling controlvalve to increase the stroking speed of the actuator. Valve and actuatorstroke speed can be amplified or increased 15 or 20 times utilizing oneor more volume boosters.

While the use of volume boosters reduces the problem of slow responsetime, it exacerbates any asymmetric performance of the valve in responseto the positioner. Asymmetry is where, for example, the actuator isunder-damped (or overshoots) in the closing direction and is over-damped(or sluggish) in the opening direction. Volume boosters not only amplifyactuator response or stroke, but also amplify the inherent asymmetry.Such asymmetry is particularly noticeable on larger volume actuatorsequipped with volume boosters.

In general, the positioner and valve system are generally operated witha low voltage electrical system. The positioner converts an electricalsignal, such as 4 mA-20 mA, to a pressure output to signal the actuator.Due to the low current flow under which the positioner operates andinternal characteristics of the positioner, the signal delivered by thepositioner to close the control valve is sent faster than the signal toopen the valve. Thus, there is an inherent asymmetry in the performanceof the positioner. The use of boosters only exacerbates this problem.

Generally, in compressor antisurge valve applications, the control valveassembly is equipped with long-stroke actuators and an equal number ofvolume boosters on the top side and the bottom side (top and bottomports or chambers, respectively) of the actuator. In one example, due tothe inherent asymmetry of the positioner and the multiple volumeboosters, the actuator response will be under-damped in the openingdirection and over-damped in the closing direction. In a fail-openactuator, i.e. where the actuator opens upon a surge condition,overshoot in the closing direction may not be particularly desirable inmany circumstances. For example, in a compressor antisurge application,overshoot in the closing direction can accidentally send a valve into asurge condition by closing the throttling valve too far or too fast orboth. It is known to those having ordinary skill in the art thatgenerally, the deleterious effects of the under-damped response arereduced by detuning the positioner so that the response in the closingdirection is critically damped. However, this detuning results in asubstantially over-damped response in the opening direction that createsa very sluggish response and is objectionable.

In general, control valve assembly performance is improved if theactuator operates with dynamic symmetry. For example, an actuatoroperates with dynamic symmetry if the dynamic response in the openingdirection of the valve is substantially the same as the dynamic responsein the closing direction.

Accordingly, continual improvements in the construction and/or operationof control valve systems and their associated components are desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic of one example of a fail-open control valveassembly constructed in accordance with the teachings of the presentinvention and employing a piston-type valve actuator.

FIG. 2 shows a detailed view, partially in cross section, of theactuator and valve of FIG. 1.

FIG. 3 shows a cross section view of the first volume boosterillustrated in FIG. 1.

FIG. 4 shows a cross section view of the second volume boosterillustrated in FIG. 1.

FIG. 5 shows a cross section view of an alternate example of the secondvolume booster illustrated in FIG. 2.

FIG. 6 shows an alternate construction of the supply port of the firstbooster.

FIG. 7 shows an alternate construction of the supply valve of the firstbooster.

FIG. 8 shows an alternate construction of the supply valve of the secondbooster.

FIGS. 9 and 10 show a graph plotting actuator percent travel andtheoretical actuator percent travel against elapsed time for a fullstroke of the actuator in one example of a control valve systemincorporating a volume booster arrangement constructed in accordancewith the teachings of the present invention.

FIG. 11 shows a second example of an asymmetric assembly using a springand diaphragm actuator.

While the disclosure is susceptible to various modifications andalternative constructions, certain illustrative embodiments thereof havebeen shown in the drawings and will be described below in detail. Itshould be understood, however, that there is no intention to limit thedisclosure to the specific forms disclosed, but on the contrary, theintention is to cover all modifications, alternative constructions, andequivalents falling within the spirit and scope of the invention asdefined by the appended claims.

DETAILED DESCRIPTION

The embodiments described herein are not intended to be exhaustive or tolimit the scope of the invention to the precise form or forms disclosed.Instead, the following embodiments have been described in order to bestexplain the principles of the invention and to enable others skilled inthe art to follow its teachings.

Referring now to the drawings, FIG. 1 illustrates one of many possibleexamples of a control valve assembly 10 using a booster arrangementconstructed in accordance with the teachings of the present invention.FIGS. 1 and particularly 2 show a valve 12 that defines a passage 14through which fluid flows. The valve 12 includes a valve plug 16 movablydisposed in a cage 18 within the valve 12. The cage 18 is perforatedsuch that fluid can pass through the cage 18. The plug 16 is connectedto a stem 20, and is moveable between a first position shown in FIG. 2in which the passage 14 is open and fluid can flow through theperforations in the cage 18, and a second position in which the plug 16is moved downward and blocks the perforations in the cage 18 such thatfluid cannot flow through the passage 14. Further, the valve 12 acts asa throttling valve so that the plug 16 can be located anywhere inbetween the first and second positions to control fluid flow through thevalve 12.

An actuator 24 is disposed adjacent the valve 12 and is configured tomove the valve 12 between the first and second positions. The actuator24 includes a cylinder 26 in which a piston rod 28 slides. The pistonrod 28 includes a piston 30 and an actuator yoke 32. The yoke 32 isoperatively connected to the stem 20 via a stem connector 33, such thatwhen the piston 28 moves, the plug 16 likewise moves. A control element22 is disposed adjacent the stem connector 33 and can sense the positionof the plug 16.

The piston 30 slides within a chamber 34 of the cylinder 26. The piston30 divides the chamber 34 into an upper chamber 36 and a lower chamber38 that are generally sealed from each other by the piston 30. A firstport 40 allows the introduction of a fluid into the upper chamber 36 anda second port 42 allows the introduction of a fluid into the lowerchamber 38.

As is known, to close the passage 14 with the valve 12, pressurizedfluid can be introduced into the upper chamber 36 through the first port40, and fluid in the lower chamber 38 can be released through the secondport 42. The piston 28 and plug 16 are then forced downward, closing thepassage 14. To open the passage 14, pressurized fluid is introduced intothe lower chamber 38 through the second port 42, and the fluid in theupper chamber 36 can be released through the first port 40. The piston28 and plug 16 are forced upward, opening the passage 14.

The upper chamber 34 is in fluid connection with a first booster 44 viaa first connection 46. The lower chamber 36 is in fluid connection witha second booster 48 via a second connection 50. Accordingly, fluidsupplied by the first booster 44 travels through the first connection 46and the first port 40 and into the upper chamber 36. Likewise, fluidsupplied by the second booster 48 travels through the second connection50 and the second port 42 into the lower chamber 38. In this example,the first and second connections 46, 50 are made of a pipe nipple, butother types of connections, such as flexible or rigid plastic, can beused. In this disclosure, the term fluid is used in the engineeringsense, and can include at least liquids and gases.

Referring back to FIG. 1, a main supply line 52 is connected to aregulator 54 and supplies the regulator 54 with pressurized fluid from apressure source such as an air compressor. The regulator 54 is in fluidconnection with and supplies pressurized fluid to the first booster 44,the second booster 48, and a positioner 56 via a first booster supplyline 58, a second booster supply line 60, and a positioner supply line62, respectively. Again, these supply lines can be made of metal tubing,rigid or flexible plastic tubing, or the like. The regulator 54 canregulate the pressure of the fluid supplied to these components.

The positioner 56 is in electrical communication with an input center63. The positioner 56 receives commands from the input center 63directing it to move the valve 12 to a desired position, i.e., theclosed position, the open position, or anywhere in between. Thepositioner 56 can be in electrical communication with the controlelement 22, and is thus able to determine the position of the plug 16within the valve 12. The positioner 56, selectively using the first andsecond boosters 44, 48, directs the movement of the valve 12 in a mannerdiscussed herein.

The positioner 56 is in fluid communication with the first booster 44via a first positioner output line 64, and is in fluid communicationwith the second booster 48 via a second positioner output line 66. Thepositioner 56 receives the electrical command input from the inputcenter 63 and converts this electrical signal to pneumatic signals. Thepositioner 56 uses the pressurized fluid from the regulator 54 todeliver the first pneumatic signal through the first output line 64 tothe first booster 44 and the second pneumatic signal through the secondoutput line 66 to the second booster 48.

If the command input directs the positioner 56 to open the valve 12 in anon-urgent manner, the positioner 56 supplies pressurized fluid throughthe second booster 48 to the lower chamber 38 of the actuator 24, andthe positioner 56 allows pressurized fluid to flow from the upperchamber 36, through the first booster 44, to be discharged to theatmosphere or a third reservoir. If the command input directs the valveto close, the reverse occurs.

As is known in the art, if the signal from the input center directs thepositioner 56 to rapidly open the valve 12 under a surge condition, thesecond pneumatic signal flows through the second booster 48 to the lowerchamber 38. The second signal also activates the second booster 48 aswill be described herein such that a large volume of pressurized fluidflows through the second booster supply line 60 through the secondbooster 48 to the lower chamber 38, thereby rapidly opening the valve12.

As detailed herein, the disclosed first and second volume boosters 44,48 include a feature that can be employed in a booster arrangement toalleviate or eliminate the aforementioned dynamic asymmetries. Theboosters 44, 48 can be arranged with other volume boosters toincorporate a functional asymmetry into the valve system to compensateor counteract the dynamic asymmetry as described below to create asystem with virtually symmetrical performance.

The first volume booster 44 disclosed herein is shown in cross sectionin FIG. 3 and the second volume booster 48 is shown in cross section inFIG. 4. The first booster 44 generally includes a casing or body 100having an inlet or supply chamber 102 and an output chamber 104 incommunication with one another via a supply port 106 within the body100. The supply chamber 102 has a supply opening 108 at one end that isopen to the exterior of the body 100. The supply chamber 102 is incommunication with the supply port 106 at its interior end. The outputchamber 104 communicates with the supply port 106 at an interior end ofthe output chamber 104 and opens to the exterior of the body 100 at anoutput opening 110. The supply chamber 102 and supply opening 108 are incommunication with the regulator 54 in the above example via the firstbooster supply line 58. The output chamber 104 is in communication withan actuator, such as the actuator 24 discussed above, via the firstconnection 46.

A bypass restriction passage 112 is in communication with the outputpassage 104 and has an adjustment screw 114. The bypass adjustment screw114 can be adjusted to permit small volumes of fluid to travel from thepositioner 56, through the first booster 44, and to the upper chamber 34of the actuator 24, as discussed below, while avoiding implementation ofthe volume boost function. A larger pressure differential across thefirst booster 44 will actuate the booster as discussed below.

A supply valve 116 is positioned within the supply chamber 102 adjacentthe supply port 106. The supply valve 116 is carried in this exampleintegrally on a portion of a stem 118 and is biased relatively tightlyto a closed position against a seat 120 of the supply port 106 by aspring 122. The spring 122 is simply a safety feature to assure thesupply valve 116 remains closed when the booster is not operating or ifa valve system failure were to occur.

A cavity 124 is provided within the body above the chambers 102 and 104and the supply port 106 in this example. A first exhaust port 126 isprovided in communication between an exhaust chamber section 128 of thecavity 124 and the output chamber 104 downstream of the supply port 106.An input signal port 130 is in fluid communication between the firstbooster supply line 58 from the positioner 56 and an upper signalchamber section 132 of the cavity 124.

A bypass port 133 provides fluid communication between the bypasspassage 112 and the input signal port 130. When the positioner sendspressurized fluid to the first booster through the input signal port 130to close the valve 12, the fluid travels into the upper signal chamber132 and through the bypass port 133. If the pressure of the fluid is nothigh enough to activate the first booster 44, as will be describedherein, the fluid travels through the bypass port 133 and the bypassrestriction passage 112, and into the output chamber 104. From there thefluid travels to the actuator 24 to close the valve 12. Of course, sincethe first booster 44 has not been activated, the closing of the valve 12takes a comparatively long time.

A floating diaphragm assembly 134 is positioned within the cavity 124and separates the cavity 124 into the exhaust and signal chambers 128and 132, respectively, and functions as a poppet valve. The diaphragmassembly 134 includes a floating manifold 136 sandwiched between a pairof diaphragms 138 and 140. The upper diaphragm 138 is called aninstrument diaphragm and defines the signal chamber 132. The lowerdiaphragm 140 is called a feedback diaphragm and defines the exhaustchamber 128. The manifold 136 includes a central opening 142 and aplurality of radial passages 144 extending radially outward therefrom.The radial passages 144 are in fluid communication with an annularpassage 146 extending around the manifold 136 between the diaphragms 138and 140. The annular passage 146 is in further fluid communication withan exhaust outlet 148 venting to atmosphere outside the body 100.

An exhaust valve 150 is carried on the valve stem 118 opposite thesupply valve 116. A second exhaust port 152 is provided in the bottom ofthe manifold 136 and provides communication between the exhaust chamber128 and the central opening 142 of the manifold 136. The exhaust valve150 bears against a seat 154 to close off the second exhaust port 152. Aspring cavity 156 is provided above the diaphragm assembly 134 andhouses a spring 158 that biases the floating assembly 134 downwardagainst the exhaust valve 150 to close the second exhaust port 152. Whenthe exhaust valve 150 is closed, the exhaust chamber 128 is not incommunication with the exhaust outlet 148. When open, the outlet chamber104 of the booster is in fluid communication with the exhaust outlet 148through the exhaust chamber 128 and diaphragm manifold 136.

Referring now to FIG. 3, the second booster 48 is depicted. In thisexample, the second booster 48 is identical to the first booster 44except for those differences noted herein. The second booster 48includes an output chamber 204 and a cavity 224 above the output chamber204. The cavity 224 and the output chamber 204 are connected by a firstexhaust port 226. In the second booster 48, the cross sectional area ofthe first exhaust port 226 is smaller than the cross sectional area ofthe first exhaust port 126 of the first booster 44. As will be seen, theresistance to flow of the exhaust through the first booster 44 is lessthan the resistance to flow of the exhaust through the second booster48.

As discussed above and referring back to the first booster 44 by way ofexample, the positioner 56 delivers a pneumatic signal converted fromelectrical impulses based on the position of the actuator 24. Thepressure signal is delivered to the signal port 130 and, thus, to thesignal chamber 132 of the booster. Further, a steady supply pressure isprovided to the supply chamber 102 by the regulator 28. The outputchamber 104 is connected to the actuator 24.

A pressure differential across the first booster 44 occurs between thesignal chamber 132 and the exhaust chamber 128 and thus the outputchamber 104 (via the first exhaust port 126). If the pressuredifferential across the booster 22 is insubstantial, as determined bythe booster bypass adjustment and as desired, each valve 116 and 150remains closed. The diaphragm assembly 134 will be in a static unloadedposition with each valve 116 and 150 born against its respective seat120 and 154. The respective springs 122 and 158 assist in biasing thevalves 116, 150 closed in an insubstantial or zero differentialcondition. A substantial pressure differential is one that is greatenough to affect the diaphragm assembly 134, whether up or down, andwill move the supply valve 116 and exhaust valve 150 in unison becauseeach is fixed to the stem 118.

During operation, a positive differential condition is achieved whenpressure is substantially greater in the signal chamber 132 than theoutput chamber 104. The positioner 56 delivers a high pressure signal tothe signal port 130. The floating diaphragm assembly 134 is forceddownward by the pressure differential upon the exhaust valve 150,keeping the second exhaust port 152 closed and opening the supply valve116. Thus, the first booster 44 provides a volume of pressurized air tothe actuator 24 from the supply chamber 102 via the output chamber 104.The output of the booster 44 is also registered on the diaphragmassembly 134 through the exhaust port 126. When the pressure in theoutput chamber 104 rises to the pressure in the signal chamber 132, thesupply valve 116 rises up and closes off.

When pressure is substantially lower in the signal chamber 132 than theoutput chamber 104, a negative pressure differential is achieved. Forexample, the positioner 56 may issue a corrective pneumatic input signalto the signal port 130 that is at a relatively low pressure. Thefloating diaphragm assembly 134 and valve stem 118 will rise. The supplyvalve 116, if not already closed, will close off the supply port 106.Once closed, the stem 118 and valves 116 and 150 will not move furtherupward. Back pressure from the output chamber 104 moves the floatingdiaphragm assembly 134 further upward against the force of the spring158 and opens the second exhaust port 152. Air in this example will ventto atmosphere from the output chamber 104 through the exhaust outlet148.

The adjustment screw 114 can be adjusted to restrict the bypass so thatdifferent pressures from the positioner will activate the booster. Forexample, if the screw 114 nearly completely blocks the bypass, a smallpressure from the positioner will activate the booster, as all thepressure will bear on the upper diaphragm 138 and force the supply valve116 downward. Likewise, if the screw 114 allows a high pressure to flowthrough the bypass, less pressure will bear on the upper diaphragm 138,and the booster will only be activated under a comparatively higherpressure from the positioner.

In volume boosters of this type, the exhaust volume is limited by thesize of the first exhaust ports 126, 226, which are the narrowest orsmallest sized passages, ports, or cavities along the exhaust path.According to the present invention, asymmetry in actuator dynamics hasbeen reduced or substantially eliminated by creating an asymmetry in thebooster exhaust volume. This is achieved by the first exhaust port 126of the first booster 44 being larger than the first exhaust port 226 ofthe second booster 48. Thus, the fluid flow resistance is greater in thesecond booster 48 than the first booster 44. In one example, the secondbooster 48 can be converted into the first booster 44 by milling orusing another method to enlarge the size of the exhaust port 226. Inthis manner, asymmetry in booster exhaust volume is achieved.

When the lower chamber 38 of the actuator 24 is filled to open thepassage 18, the second booster 48 can be employed to boost the strokespeed to a greater degree. The first booster 44 has a larger firstexhaust port 126 to provide a greater exhaust volume capacity for therelease of the air within the upper chamber 36. This can reduce dampingduring the opening of the valve. The amount of damping can be controlledby both the number of boosters assisting the actuator side, as well asthe size difference between the exhaust ports 126, 226 of the boosters44 and 48.

When the upper chamber 36 of the actuator 24 is filled to close thepassage 18, the first booster 44 can be employed to boost the strokespeed, but to a lesser degree. The second booster 48 provides a lessercapacity for volume exhaust, and thus a slightly greater damping effectduring the closing stroke than the first booster 44 provides during theopening stroke.

The difference in size of the booster exhaust ports 126 and 226 can beemployed to counteract the inherent asymmetrical dynamics created inlarge volume actuators and valve systems. Thus, when a system has anasymmetrical performance in which the closing stroke is faster than theopening stroke, the first and second boosters 44, 48 can be used toincrease the exhaust in the opening stroke such that symmetricalperformance can be achieved.

The actuator as disclosed in this example need not be of a piston type,but can be virtually any type of actuator. For example, the actuator canbe a spring and diaphragm type actuator. Further, the system can employmultiple volume boosters for each side of the actuator, if desired. Itmay be preferable to employ the same number of boosters on each side ofthe actuator to create near symmetry in boost and dynamic performanceduring each stroke. The asymmetrical booster exhaust size as disclosedherein can be employed in one or more of the boosters on either side ofthe actuator to achieve the desired amount of compensation for theasymmetric dynamics. Further, other structures can be employed toprovide an asymmetric functionality of the boosters 44, 48 to counteractthe asymmetric performance. This can include any structure that createsdifferent flow resistance such as using the same boosters, but placing aregulator on one side to restrict exhaust, or any other structure,internal or external to the boosters themselves that affect the flowresistance of the supply or exhaust.

In the example shown, the first exhaust port 126 and the second exhaustport 226 are shown as having a circular cross section and cylindricalwith the first exhaust port 126 having a larger diameter than the secondexhaust port 226. In this manner, the resistance to fluid flow isgreater in the second booster 48 than in the first booster 44. However,it will be seen that any number of constructions can be created toincrease or decrease fluid flow. These include placing an obstruction inthe path of an exhaust port such as a tab, a block, a bar, a vent, afan, or the like. The second exhaust port 226 could also includeirregular edges to increase the resistance to fluid flow. This caninclude threading the hole, creating a polygonal cross section or thelike. Other obstructions and irregularly shaped sidewalls will be knownby those of ordinary skill in the art.

In an alternate embodiment of the second booster 48, a third booster 300is depicted in FIG. 5 showing another manner of increasing the fluidflow resistance. The third booster 300 includes a third exhaust port 326that is longer in length than the first exhaust port 126. The firstexhaust port 126 and the third exhaust port 326 are each circular incross section with the same diameter, however the length of the thirdexhaust port 326 is longer than the length of first exhaust port 126. Toincrease the resistance further, the third exhaust port 326 could have acurved or serpentine design. In this example the volume of a thirdoutput chamber 304 is decreased, but other designs can be made that donot decrease the volume of the third output chamber 304. In general, anydesign that restricts the exhaust fluid flow through the second booster48 (or third booster 300) relative to the first booster 44 isappropriate.

In another example, shown in FIG. 6, instead of restricting the exhaustpath to create an asymmetry, the resistance to airflow in the supplypaths of the two boosters can be asymmetric. To this end, the crosssection of the supply port 106 a in the first booster 44 can be smallerthan the supply port 206 of the second booster 48. In this example, theinherent asymmetry is counteracted by supplying fluid to the actuator 24at a greater mass flow rate through the second booster than the first.Of course, the exhaust ports can also be manipulated in addition to thesupply ports.

In a further method of manipulating the flow through the first booster44, the construction of the supply valve 116 can be changed. The shapeof the supply valve 116 as shown in FIG. 3 is that of a cone. Instead,as shown in FIG. 7, the supply valve 116 a could take the shape of abell to further restrict fluid flow rate through the supply port 106 atlow amplitudes. In contrast, as shown in FIG. 8, the supply valve 216 aof the second booster 48 could take the shape of a flat plate toincrease the flow rate.

FIGS. 9 and 10 illustrate an example of a system and a system outputthat can be achieved by employing the asymmetric volume boosterarrangement disclosed herein. The solid lines in each plot representtheoretically perfect symmetry. The dashed lines represent actual testedperformance for different arrangements.

FIG. 9 illustrates an example of stroke speed for one stroke cycle invarious booster/actuator/valve size combinations. In each plot, it canbe seen that a 100% stroke can be achieved in about 1 and less than 2seconds. Each test utilized a four volume booster arrangement with twovolume boosters on each side of the actuator.

FIG. 10 illustrates that long stroke and reverse stroke cycles can beachieved with substantial dynamic symmetry utilizing the disclosedbooster arrangement. The left axis of each plot represents percent offull stroke. The bottom axis of each plot represents elapsed time. Theseplots show long stroke and reverse stroke cycles and illustrate thesubstantial symmetry of the valve performance achieved using thedescribed system 10.

FIG. 11 discloses another example in which an asymmetric design is usedon a spring and diaphragm actuator 500. The actuator 500 is attached toa valve 502 similarly as in previous examples. The actuator includes ahousing 504 in which a diaphragm 506 is disposed. The diaphragm 506 isconnected to an actuator yoke 508, which is connected to the valve 502.The diaphragm 506 and the housing 504 define an upper chamber 510. Fluidpressure within the upper chamber 510 forces the diaphragm 506 andtherefore the yoke 508 and valve 502 downward. When the fluid pressurein the upper chamber 510 is lowered, a spring 512 pushes the diaphragm506 back upward. As can be seen, no air pressure is used to push thediaphragm 506 upward. Thus, an asymmetric response can be created in theperformance of this actuator 500 by this construction alone.

In this example, a positioner 514 supplies fluid to a first booster 516and a second booster 518 in parallel. The first and second boosters 516,518 are in fluid connection to the upper chamber 510 of the actuator500. Only the first booster 516 is connected to a pressurized fluidsource through line 520 so that when the signal from the positioner 514activates the boosters 516, 518, only the first booster 516 supplieshighly pressurized fluid to the upper chamber 510 of the actuator 500.However, when the signal from the positioner 514 is lowered, the forceof the spring 512 pushes the diaphragm 506 upward, and the pressurizedfluid within the upper chamber 510 is exhausted through both the firstand second boosters 516, 518. The fluid flow rates through the first andsecond boosters 516, 518 can be manipulated as described above, such asby enlarging or shrinking either the fluid supply path or the fluidexhaust path. In general, the fluid supply path is constricted relativeto the fluid exhaust path. For example, the fluid supply path in thefirst booster 516 may have a supply constricted portion, and the firstfluid exhaust path in the first booster and the second fluid. exhaustpath in the second booster may each have a first and second exhaustconstricted portion. The supply constricted portion may have a smallercross sectional area than the combined cross sectional areas of thefirst and second exhaust constricted portions. Other techniques outlinedherein can also be used. In this manner, dynamic symmetry of performancecan be achieved in a spring and diaphragm actuator 500.

The above-described details in the various Figures need not be mutuallyexclusive. That is, in accordance with the spirit and scope of theexamples disclosed herein, one may pick and choose various aspects ofthe several Figures and combine those selected aspects with otherselected aspects illustrated and described with respect to differentFigures.

Numerous modifications and alternative embodiments of the invention willbe apparent to those skilled in the art in view of the foregoingdescriptions. Accordingly, these descriptions are to be construed asillustrative only and are for the purpose of teaching those skilled inthe art the best mode or modes presently contemplated for carrying outthe invention. The details of the structure or structures disclosedherein may be varied substantially without departing from the spirit ofthe invention, and the exclusive use of all modifications which comewithin the scope of the appended claims, either literally or under thedoctrine of equivalents, is reserved.

1. An asymmetric volume booster assembly, comprising: an actuatormovable in a first direction and a second direction; a first booster influid communication with the actuator, the first booster including afirst supply passage and a first exhaust passage, wherein the firstsupply passage supplies fluid to the actuator and the first exhaustpassage exhausts fluid from the actuator, the first exhaust passageconfigured to produce a first fluid flow resistance; and a secondbooster in fluid communication with the actuator, the second boosterincluding a second supply passage and a second exhaust passage, whereinthe second supply passage supplies fluid to the actuator and the secondexhaust passage exhausts fluid from the actuator, the second exhaustpassage configured to produce a second fluid flow resistance; whereinthe first fluid flow resistance is greater than the second fluid flowresistance, such that the actuator moves substantially symmetrically inthe first direction and the second direction; wherein the first exhaustpassage includes a first constricted portion, and the second exhaustpassage includes a second constricted portion, the first constrictedportion having a smaller cross sectional area than the secondconstricted portion; and wherein the first exhaust passage includes afirst output chamber, a first exhaust port, a first exhaust chamber, afirst manifold including passages, and a first exhaust outlet, thesecond exhaust passage includes a second output chamber, a secondexhaust port, a second exhaust chamber, a second manifold includingpassages, and a second exhaust outlet, and wherein the first exhaustport defines the first constricted portion, and the second exhaust portdefines the second constricted portion.
 2. The assembly of claim 1, thefirst booster further comprising a first signal port and the secondbooster further comprising a second signal port, wherein when airpressure is greater in the first output chamber than in the first signalport, the air pressure forces a first manifold upward, thereby openingthe first exhaust passage while maintaining the first supply passageclosed, wherein when air pressure is greater in the second outputchamber than in the second signal port, the air pressure forces a secondmanifold upward, thereby opening the second exhaust passage whilemaintaining the second supply passage closed.
 3. The assembly of claim1, the actuator comprising a piston moveable in a first direction and asecond direction, wherein the first booster is adapted to supply fluidto the actuator to move the piston in the first direction, and thesecond booster is adapted to supply fluid to the actuator to move thepiston in the second direction, wherein the resistance to fluid flowfrom the actuator through the first booster is greater than theresistance to fluid flow from the actuator through the second boostersuch that the assembly achieves generally symmetrical performance.
 4. Anasymmetric volume booster assembly, comprising: an actuator movable in afirst direction and a second direction; a first booster in fluidcommunication with the actuator, the first booster including a firstsupply passage and a first exhaust passage, wherein the first supplypassage supplies fluid to the actuator and the first exhaust passageexhausts fluid from the actuator, the first exhaust passage configuredto produce a first fluid flow resistance; and a second booster in fluidcommunication with the actuator, the second booster including a secondsupply passage and a second exhaust passage, wherein the second supplypassage supplies fluid to the actuator and the second exhaust passageexhausts fluid from the actuator, the second exhaust passage configuredto produce a second resistance to fluid flow; wherein the first fluidflow resistance is greater than the second fluid flow resistance, suchthat the actuator moves substantially symmetrically in the firstdirection and the second direction; and further comprising a positioner,a first line from the positioner to the first booster and a second linefrom the positioner to the second booster, wherein the positionerselectively signals the first and second boosters with pressurized fluidthrough the first and second lines, with a first and second signal,respectively, wherein the delivery of the first signal is slower thanthe delivery of the second signal.
 5. The assembly of claim 4, whereinthe first exhaust passage and the second exhaust passage each includes apair of chambers separated by an exhaust port, and wherein the exhaustport of the first booster is longer than the exhaust port of the secondbooster.
 6. The assembly of claim 4, wherein the first exhaust passagehas a cross sectional area similar to a cross sectional area of thesecond exhaust passage.
 7. An asymmetric volume booster assembly,comprising: an actuator movable in a first direction and a seconddirection; a first booster in fluid communication with the actuator, thefirst booster including both a supply passage and an exhaust passage,wherein the supply passage supplies fluid to the actuator and theexhaust passage exhausts fluid from the actuator; a first supply valvedisposed in the first booster for controlling fluid flow through thefirst booster and toward the actuator; a second booster in fluidcommunication with the actuator, the second booster including a supplypassage and an exhaust passage, wherein the supply passage suppliesfluid to the actuator and the exhaust passage exhausts fluid from theactuator; a second supply valve disposed in the second booster forcontrolling fluid flow through the second booster and toward theactuator; wherein the first supply valve has a higher fluid flowresistance than the second supply valve; and wherein the first supplyvalve is bell-shaped and the second supply valve comprises a flat plate.8. The assembly of claim 7, wherein the first supply valve is disposedin a supply port configured to restrict fluid flow.
 9. An asymmetricvolume booster assembly, comprising: an actuator movable in a firstdirection and a second direction; a first booster in fluid communicationwith the actuator, the first booster including a first supply passageand a first exhaust passage, wherein the first supply passage suppliesfluid to the actuator and the first exhaust passage exhausts fluid fromthe actuator; a second booster in fluid communication with the actuator,the second booster including a second exhaust passage, wherein thesecond exhaust passage exhausts fluid from the actuator; wherein thecombination of the first and second exhaust passages has a lowerresistance to fluid flow than the first supply passage such that dynamicsymmetry of operation of the actuator is provided and wherein theactuator comprises a housing and a diaphragm disposed within thehousing, the diaphragm dividing the housing into an upper chamber and alower chamber and being moveable in the first direction toward the lowerchamber and the second direction toward the upper chamber, and a springdisposed in the lower chamber and biasing the diaphragm away from thelower chamber, wherein the first booster supplies fluid to the upperchamber to move the diaphragm in the first direction, and the springmoves the diaphragm in the second direction upon release of the fluid inthe upper chamber.
 10. The assembly of claim 9, wherein the first supplypassage includes a first constricted portion, and the first and secondexhaust passages each include a second and third constricted portion,respectively, the first constricted portion having a smaller crosssectional area than the total cross sectional area of the second andthird constricted portions.
 11. The assembly of claim 10, wherein thefirst, second and third constricted portions each have a circular crosssection.
 12. The assembly of claim 10, wherein the first constrictedportion includes irregular edges to increase the flow resistance. 13.The assembly of claim 10, wherein the first constricted portion includesan obstruction element disposed in the first supply passage.